Cuiping Zeng

Photocatalytically improved azo dye reduction in a microbial fuel cell with rutile-cathode.

Reductive decolorization of azo dye in wastewater was investigated in a dual-chamber microbial fuel cell (MFC) equipped with cathodes made of graphite or rutile-coated graphite. Rapid reduction of methyl orange (MO) with concomitant electricity production was achieved when the rutile-coated cathode was irradiated by visible light. The electrochemical impedance spectra (EIS) indicate that the polarization resistance (R(p)) of the rutile-cathode MFC decreased from 1378 Omega in dark to 443.4 Omega in light, demonstrating that photocatalysis of rutile can enhance the cathodic electron transfer process. The combination of the biologically active anode and photocatalysis-supported cathodic reduction of MO obeyed the pseudo-first-order kinetics. The analysis of decolorization products indicates that the azo bond of MO was probably cleaved by photoelectrons at the irradiated rutile-cathode, resulting in the products of colorless hydrazine derivatives. In addition, concurrently enhanced electricity generation in the MFCs involving photocatalyzed cathodic reduction of MO was observed throughout this study.

Growth of non-phototrophic microorganisms using solar energy through mineral photocatalysis

Phototrophy and chemotrophy are two dominant modes of microbial metabolism. To date, non-phototrophic microorganisms have been excluded from the solar light-centered phototrophic metabolism. Here we report a pathway that demonstrates a role of light in non-phototrophic microbial activity. In lab simulations, visible light-excited photoelectrons from metal oxide, metal sulfide, and iron oxide stimulated the growth of chemoautotrophic and heterotrophic bacteria. The measured bacterial growth was dependent on light wavelength and intensity, and the growth pattern matched the light absorption spectra of the minerals. The photon-to-biomass conversion efficiency was in the range of 0.13-1.90‰. Similar observations were obtained in a natural soil sample containing both bacteria and semiconducting minerals. Results from this study provide evidence for a newly identified, but possibly long-existing pathway, in which the metabolisms and growth of non-phototrophic bacteria can be stimulated by solar light through photocatalysis of semiconducting minerals.

Graphene oxide and H2 production from bioelectrochemical graphite oxidation.

Graphene oxide (GO) is an emerging material for energy and environmental applications, but it has been primarily produced using chemical processes involving high energy consumption and hazardous chemicals. In this study, we reported a new bioelectrochemical method to produce GO from graphite under ambient conditions without chemical amendments, value-added organic compounds and high rate H2 were also produced. Compared with abiotic electrochemical electrolysis control, the microbial assisted graphite oxidation produced high rate of graphite oxide and graphene oxide (BEGO) sheets, CO2, and current at lower applied voltage. The resultant electrons are transferred to a biocathode, where H2 and organic compounds are produced by microbial reduction of protons and CO2, respectively, a process known as microbial electrosynthesis (MES). Pseudomonas is the dominant population on the anode, while abundant anaerobic solvent-producing bacteria Clostridium carboxidivorans is likely responsible for electrosynthesis on the cathode. Oxygen production through water electrolysis was not detected on the anode due to the presence of facultative and aerobic bacteria as O2 sinkers. This new method provides a sustainable route for producing graphene materials and renewable H2 at low cost, and it may stimulate a new area of research in MES.

Enhanced Alcaligenes faecalis Denitrification Rate with Electrodes as the Electron Donor.

ABSTRACT The utilization by Alcaligenes faecalis of electrodes as the electron donor for denitrification was investigated in this study. The denitrification rate of A. faecalis with a poised potential was greatly enhanced compared with that of the controls without poised potentials. For nitrate reduction, although A. faecalis could not reduce nitrate, at three poised potentials of +0.06, −0.06, and −0.15 V (versus normal hydrogen electrode [NHE]), the nitrate was partially reduced with −0.15- and −0.06-V potentials at rates of 17.3 and 28.5 mg/liter/day, respectively. The percentages of reduction for −0.15 and −0.06 V were 52.4 and 30.4%, respectively. Meanwhile, for nitrite reduction, the poised potentials greatly enhanced the nitrite reduction. The nitrite reduction rates for three poised potentials (−0.06, −0.15, and −0.30 V) were 1.98, 4.37, and 3.91 mg/liter/h, respectively. When the potentials were cut off, the nitrite reduction rate was maintained for 1.5 h (from 2.3 to 2.25 mg/liter/h) and then greatly decreased, and the reduction rate (0.38 mg/liter/h) was about 1/6 compared with the rate (2.3 mg/liter/h) when potential was on. Then the potentials resumed, but the reduction rate did not resume and was only 2 times higher than the rate when the potential was off.

Synergistic Interaction between Electricigens and Natural Pyrrhotite to Produce Active Oxygen Radicals

In this work we demonstrated that the active oxygen radicals could be produced by the synergistic interaction between electricigens and natural pyrrhotite. The identification of such an interactive pathway was conducted by using a fuel cell-type design, in which the electricigen-attached carbon felt electrode was used as the anode and the pyrrhotite-coated graphite electrode was used as the corresponding cathode. Current density, polarization and power density curves obtained at different treatments demonstrated the synergistic effects of electricigens and pyrrhotite improved the electrons transfer rate between them. Cyclic voltammetry (CV) analysis showed the reductive peaks of O2/H2O2 at 0.88 V (vs. SCE, saturated calomel electrode) and ionic and structural Fe(III)/Fe(II) at 0.31 V (vs. SCE) and 0 V (vs. SCE), respectively. The electrochemical results indicated the electricigen-assisted pyrrhotite photoelectrochemical reactions gave rise to Fentons reagents: Fe2+ and H2O2, which underwent a further reaction to generate active oxygen radical ·OH. By using N, N-dimethyl-p-nitrosoaniline discoloration as a model reaction, the ·OH production rate at the pyrrhotite-cathode was found to follow the first-order kinetics. Practical application of the synergistic interaction between the electricigen and natural pyrrhotite to a real old-aged landfill leachate degradation resulted in 78% chemical oxygen demand (COD) removal and 77% decolourization efficiency. The current generation lasted more than 45 days verified the validity of such system in long-term operation. The proposed interactive pathway would be expected as an alternative cost-effective technology for future wastewater treatment.

Photoelectrochemical performance of birnessite films and photoelectrocatalytic activity toward oxidation of phenol

Birnessite films on fluorine-doped tin oxide (FTO) coated glass were prepared by cathodic reduction of aqueous KMnO4. The deposited birnessite films were characterized with X-ray diffraction, Raman spectroscopy, scanning electron microscopy and atomic force microscopy. The photoelectrochemical activity of birnessite films was investigated and a remarkable photocurrent in response to visible light was observed in the presence of phenol, resulting from localized manganese d-d transitions. Based on this result, the photoelectrocatalytic oxidation of phenol was investigated. Compared with phenol degradation by the electrochemical oxidation process or photocatalysis separately, a synergetic photoelectrocatalytic degradation effect was observed in the presence of the birnessite film coated FTO electrode. Photoelectrocatalytic degradation ratios were influenced by film thickness and initial phenol concentrations. Phenol degradation with the thinnest birnessite film and initial phenol concentration of 10mg/L showed the highest efficiency of 91.4% after 8hr. Meanwhile, the kinetics of phenol removal was fit well by the pseudofirst-order kinetic model.

Electrochemical Interaction of a Heterotrophic Bacteria Alcaligenes faecalis with a Graphite Cathode

This study focused on the electrochemical interaction between a heterotrophic bacterium, Alcaligenes faecalis and a graphite cathode. The growth of Alcaligenes faecalis on the cathode surface was found to be stimulated by applying a polarization potential of −0.25 V (vs. SCE) to the cathode. Environmental scanning electron microscope (ESEM) showed a significant increase of the bacterial population on the poised-potential electrode and a notable change of the bacterial morphology from short rod to unusual long rod shape. Cyclic voltammetry (CV) curves of the biofilm-attached electrode showed two reductive peaks at around 0.4 V and −0.35 V vs. SCE, which were assigned to the redox potentials of outer membrane cytochromes and attached metabolites, respectively. Electrochemical impedance spectroscopy (EIS) indicated the attachment of active Alcaligenes faecalis reduced the charge transfer resistance of the electrode. The results conclusively indicated that both the bacteria and the metabolites on the electrode were involved in the electrochemical reactions, and Alcaligenes faecalis was bioelectrochemically active in cathodic electron transfer process.